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Author Affiliations

2Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro,
Portugal

3World Class University (WCU) Program of Chemical Convergence for Energy and Environment (C2E2), School of Chemical and Biological Engineering, College of Engineering, Seoul National University (SNU), Seoul 151-744,
Korea

Abstract

Owing to the competition between the radiative and non-radiative decay channels occurring in plasmonic assemblies, we show here how to conceive a long pass emission filter and actually design it. We report the synthesis of gold@silica nanoparticles grafted with dye molecules. The control of the thickness of the silica shell allows us to tune the distance between the metal core and the dye molecules. Assemblies of small number (1 to 7) of these core-shell (CS) particles, considered as multimers, have also been produced for the first time. We show that the shaping of the emission spectra of the multimers is drastically enhanced by comparison with the corresponding monomers. We also show a strong enhancement of the decay rates at the LSP resonance, dominated by the non-radiative energy tranfer from the active medium to the metal. The decay rates decrease as the detuning between the long wavelength emission and the LSP resonance increases.

Fig. 2 (a) Simulated reflectivity spectra of monomers, trimers in line and heptamers with gold core diameter of 60 nm and silica shell thickness of 10, 20 and 30 nm, respectively. (b) LSP resonance as a function of the number of monomers coupled in a multimer for a silica shell thickness ranging from 10, 20 to 30 nm, respectively. Solid lines are linear fits of the LSP resonances as a function of the number of monomers coupled in a multimer. Non-radiative, radiative and total enhancement rates (c) as well as the apparent quantum yield (d) as a function of wavelength for dimers with a shell varying from 10 to 20 and 30 nm, respectively.

Fig. 6 Decay profiles as a function of wavelength for RITC molecules (a), CS+3 monomers (b) and CS+3M multimers in ethanol (c). The solid lines are convoluted stretched exponentials fits with the instrumental response function of the setup of the various decay profiles.

Fig. 7 Decay times as a function of silica shell thickness, 10 (a), 20 (b) and 30 nm (c) and as a function of the emission wavelength for the monomers CS+ and multimers CS+M. Also shown for comparison are the wavelength-independent decay times of pure RITC molecules in ethanol.The solid lines are linear fits of the decay times as a function of wavelength.

Fig. 8 Decay rate enhancement gt (λ) as a function of silica shell thickness (10, 20 and 30nm) and as a function of the emission wavelength for the multimers CS+1M, CS+2M and CS+3M. The solid lines are fits
gt(λ)∝1λ of the decay times as a function of wavelength.